This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Beta-lactams are the most common antibiotics in clinical use and represent more than 60% of total world consumption of antimicrobial drugs. They include penicillins, cephalosporins, monobactams, penems and carbapenems, and over 50 antibiotics of this class are available on the market. Over 60 years of extensive and sometimes uncontrolled use of antibiotics has resulted in selection and world-wide spread of resistant microorganisms, and this poses a serious threat to the antibiotic therapy of infectious diseases. A major mechanism of bacterial resistance to beta-lactam antibiotics is the production of beta-lactamases, enzymes that hydrolyze the conserved four-membered ring of beta-lactams, rendering them inactive. We are currently working on two recently-discovered beta-lactamase enzymes. The first, named GES-1 (Guiana Extended-Spectrum, after the country where it was first isolated) was initially described in 2000. This ESBL is very distantly related to other class A beta-lactamases and produces resistance to penicillins and first- second-, and some third-generation cephalosporins (e.g. ceftazidime) but not to monobactams and carbapenems. Since 2000, nine GES-type enzymes (GES-1 - GES-9) from different geographical locations have been described. The most alarming characteristic of the GES family of enzymes that distinguish them from the TEM and SHV superfamilies, is their apparent ability to evolve into weak carbapenemases, enzymes capable of hydrolyzing carbapenem antibiotics. The second enzyme, Oih-1 was isolated from a bacterium Oceanobacillus iheyensis found in a deep-sea mud near Japan. The native enzyme has been crystallized and the structure was determined by molecular replacement using the beta-lactamase from the mesophilic Bacillus stearothermophilus as the search model. A comparative analysis of the cold-stable and mesophilic structures shows an increased number of acidic amino acids in the Oih-1 enzyme, with a increased clustering of these residues at the molecular surface.